Update hetzner_nfs.md

[browneye253]

Added an info note about a potential problem with the feederbox storage array mounting. I also added a small note explaining a way to confirm the setup worked on the mediabox.

Please describe the purpose of this Pull Request.

For new Sandbox app/role documentation, please confirm you have completed the following tasks:

• [] App documentation page created
• [] markdownlint reports no errors on edited page(s) - use https://dlaa.me/markdownlint/ if your IDE does not have this built in
• [] Reference added in docs/sandbox/index.md
• [] Reference added in mkdocs.yml nav menu

[saltydk]

Not sure I agree with the note about the mounting paths, the recommendation is to mount a storage array at /mnt.

[saltydk]

main branch has been archived.